The present invention relates to a catalyst structure comprising a substrate having protruding catalyst support particles permanently fixed into the surface of the substrate with a catalyst deposited thereon and to the method of manufacture.
Catalyst structures have been disclosed in the prior art which involve the placement of catalyst materials onto the surface of a substrate. At least one of the uses for these prior art catalytic structures is for the conversion of atmospheric ozone to molecular oxygen as well as the conversion of other airborne pollutants such as carbon monoxide and unburned hydrocarbons into harmless compounds such as carbon dioxide and water vapor. One particular use has been for the construction of automotive heat exchangers such as radiators and air conditioning condensers.
U.S. Pat. No. 4,206,083 discloses the co-precipitation of platinum, palladium and manganese oxide on a ceramic support forming a catalyst for the decomposition of ozone in air. The ceramic support is impregnated with a solution containing the precursors of the desired catalyst. The impregnated support is then dried and heated to produce platinum and palladium metal and manganese oxide.
In U.S. Pat. No. 4,343,776, an ozone abatement catalyst is described having a carrier or support of a porous refractory skeletal structure or metal monoliths of aluminum or other materials preferably having a plurality of flow-through channels. A platinum group metal and a non-precious Group VIII metal oxide or aluminate, such as an oxide or aluminate of iron, cobalt and nickel, are applied to the external surface of the carrier or support with the metal oxide or aluminate being applied with an alumina slip preferably prior to the application of the platinum group metal.
U.S. Pat. No. 5,187,137 likewise discloses an ozone decomposing catalyst comprising a manganese oxide together with palladium or palladium oxide formed as a thin film on a support. The support may be formed from various metal oxides or it may be a metal support. The catalyst is applied to the support as a thin film preferably with an alumina sol as a binder.
Another catalyst composition which is described as being adapted for ozone abatement is disclosed in U.S. Pat. No. 5,422,331. This catalytic material comprises a substrate, which may be aluminum, with an undercoat layer containing a mixture of fine particulate refractory metal oxide and a sol such as a silica sol providing good adherence to the substrate. An overlayer also contains a refractory metal oxide on which is dispersed a catalytic metal component, such as palladium and manganese components, which is then calcined.
U.S. Pat. No. 5,997,831 specifically discloses a method of treating the atmosphere to convert pollutants such as ozone, hydrocarbons and carbon monoxide to harmless compounds involving contacting the atmosphere with a heat exchanger which has an outer surface coated in selected areas with a catalytic layer. The catalyst may be manganese oxide and/or precious metals applied by dipping or spraying and the catalytic layer is coated with a porous protective coating such as a polymer.
Another catalyst structure is disclosed in the copending U.S. patent application Ser. No. 09/590,736 filed Jun. 8, 2000 by the inventors of the present application in which catalyst particles are dispersed over and forged into the surface of a metal substrate member with the catalyst particles protruding from and fixed to the substrate.
The present invention relates to a method of forming a catalytic structure particularly suited to the treatment of the atmosphere to remove atmospheric pollutants. The invention relates specifically to the formation of catalysts for the decomposition of ozone to form molecular oxygen but is also applicable to catalyst materials for a range of other reactions including, for example, the decomposition of hydrocarbons and the oxidation of carbon monoxide. An object of the invention is to provide an improved method of forming a metal substrate having a surface with particles dispersed over and fixed to the surface which protrude from the surface and which comprise a support and a catalytic material.
The invention involves forming a catalytic structure having catalyst support particles dispersed over and forged into the surface of a substrate member whereby the particles are protruding from and permanently fixed to the substrate. The substrate is a metal sheet or body, preferably aluminum or copper. A slurry containing catalyst support particles which are capable of being forged into the surface of the substrate is applied to the surface of the substrate and the particles are pressed against the surface of the substrate to fixedly forge the particles into the surface. The substrate is preferably in web form and the slurry is continuously applied. Pressing the particles against the surface is preferably accomplished with a rotating brush, a fabric or so-called molleton roller or solid rollers such as a solid metal roller or hard rubber roller. The catalyst support particles may comprise any particulate material which is capable of absorbing and supporting the catalyst material and which is capable of being forged into the substrate surface. The catalyst material is then applied to the forged catalyst support particles.